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    <title>Document</title>
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<body>
    <script>
        var str = "hello"
        var arr = str.split('');
        console.log(arr.reverse().join(""));
    </script>

<script>
    var a = [1,2,3,4,5,6,7,8,9];
    var b=[];
    for( let i=0;i<a.length;i+=3){
        console.log(a.slice(i,i+3));
        b.push(a.slice(i,i+3).join(""))
    }
    console.log(b);
</script>
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